How many of you have ever had a head gasket THAT YOU INSTALLED on one of our little air cooled engines fail?
I have taken in some motors over the years with bad head gaskets - unknown history/repairs/can't say what happened. And one that I DID that failed because of a bad head (gas cut from previous blown gasket) - I figured it wasn't going to work but did it anyway (ohh to be young and stupid again....). But thinking back, I don't remember ever having a gasket fail (on an air cooled engine) because of the gasket - either a new one or a reused one!
Usually, when they DO fail, its a warped head or wrong torque (too high is just as bad as too low...). Less likely, would be poor surface prep/install or using a gasket that was beyond its lifespan.
The design of these engines (large squish bands, low compression, lots of studs/fasteners) make them pretty hardy and forgiving of minor imperfections. Multiple in-line cylinders and water cooled engines are more critical of the gasket and require more attention/precision.
"My opinion" - If you have the mechanical ability to take the head off and LOOK at the head gasket/mating surfaces ( ), you can tell if the gasket is re-usable. Gaskets don't "wear out" and will usually be fine unless damaged in removal. Prep and checking for other issues is critical though.
Nothing wrong with going with "new" and erring on the safe side, but I don't think it is always REQUIRED.
BTW - gaskets aren't always cheap anymore - a set of oem gaskets for a magnum will run around $60!!! You can get them cheaper, but that's the price through kohler...